[Vantage-Point]

Hello Everyone,
Can a tele-converter (1.4x) be used with a zoom lens ex. DA 55-300 or Tamron 70- 200 or does it have to be a tele prime , or can it be used with both? Who (Sigma, Tamron) has a good one?

[Adam]

It can be used with either. The only problem is that zoom lenses generally have slower aperture, so you'll have less light to work with (in general). With the 1.4x your 55-300mm will go from being F4-5.8 to F5.6-F8.2 ish, so expect the VF to be a little darker. Totally usable, though

[excanonfd]

You can use a TC with any lens you like but I wouldn't recommend a TC with any slow entry level zoom lenses because you would lose AF at the longer focal lengths.

[RioRico]

CAN a TC be used with a zoom? Sure thing!
SHOULD a TC be used with a zoom? Nope.

Except for high-end TCs matched to high-end teles, you're mostly better off just cropping the image to achieve a narrower-FOV effect. That's the optics / image-quality function. The mechanisms are something else. We have a few basic kinds of TCs for PK mount:

* M-type, with only a mechanical aperture linkage -- pretty cheap
* A-type, with electrical contacts for aperture control -- fairly cheap
* AF, with A-type contacts and an AF drive screw -- not cheap at all!!
* a rare Pentax TC that will slowly AF with MF lenses -- nope, not cheap

If you can afford an AF-TC, you can afford better lenses too. I can just about guarantee you won't be real happy with an M- or A-type TC on your AF zooms. They'll work fine with stop-down metering, and should stay within metering range. With an M-type, you'll want to be in M mode and use the Green button. But unless you're comfortable with manual shooting, they'll be clumsy.

My recommendation: Unless you're shooting for surveillance or blackmail, use what you have, and crop.

[Ira]

Three word answer, plus a comma:

Yeah, but don't

[reeftool]

Sigma has a TC that works quite well with a couple of their higher end zooms. Those TC's were made to work with those lenses. As a general rule, the other posts are correct and TC's will probably degrade the IQ a lot. That said, most of us own or have owned a TC and have tried them on every lens we own. Sometimes a TC works very well with a particular lens. Just don't buy one expecting it to.

[Lowell Goudge]

At present, there are only a few options for TCs and tele zooms.

The sigma tele zooms such as the 70-200f2.8 and similar fast tele zooms as well as primes can work with the sigma TCs but only the screw drive lenses, the TCs have not been made for HSM lenses at this point. These TCs require the lens design to be somewhat specific, with a 35 mm diameter 12 mm deep recess in the rear of the lens.

On lenses with combined aperture of 6.7 or greater AF won't work

The other option is the pentax 1.7x AF TC which can work on all lenses that are F4 or faster, but this converts them into semi aF lenses

[altovintner]

CAN a TC be used with a zoom? Sure thing!
SHOULD a TC be used with a zoom? Nope.

Except for high-end TCs matched to high-end teles, you're mostly better off just cropping the image to achieve a narrower-FOV effect. That's the optics / image-quality function. The mechanisms are something else. We have a few basic kinds of TCs for PK mount:

* M-type, with only a mechanical aperture linkage -- pretty cheap
* A-type, with electrical contacts for aperture control -- fairly cheap
* AF, with A-type contacts and an AF drive screw -- not cheap at all!!
* a rare Pentax TC that will slowly AF with MF lenses -- nope, not cheap

If you can afford an AF-TC, you can afford better lenses too. I can just about guarantee you won't be real happy with an M- or A-type TC on your AF zooms. They'll work fine with stop-down metering, and should stay within metering range. With an M-type, you'll want to be in M mode and use the Green button. But unless you're comfortable with manual shooting, they'll be clumsy.

My recommendation: Unless you're shooting for surveillance or blackmail, use what you have, and crop.

Hello RioRico. Great post. Agree with your conclusion.

I have tried a Tamron 1.4x TC with my 55-300 DA L zoom and the results are not satisfactory.

[rvannatta]

Three word answer, plus a comma:

Yeah, but don't

Amen!

[jon pafford]

look at review

http://www.google.com/url?sa=t&rct=j&q=tamron%20tc%20converter%20pics%20&sou...B0jZS9fWeYj42w

[Lowell Goudge]

I think it all depends on the lens and TC used.

I have attache 2 shots, posted previously, using the Sigma APO70-200F2.8 EX (non DG non macro) and sigma APO 2X EX DG teleconverter.

You be the judge.

first is a fill frame shot no cropping, second is about 10% of the total image area

Both are with the K10D





the second shot was hand held, from a boat a long way away.

This is a combination that seems to work well, at least for me, but I will make note of the fact that even in many lens reviews, this is the sharpest of all the sigma 70-200F2.8 zooms at 200mm. Later lighter and closer focusing models and the first HSM models are reported to be a little soft at 200.

Using a good quality TC on the specific series of lenses it is designed for can be an acceptable option. I would not try this with other lenses necessairly. Having said that, however, and in reading the design approach of the origonal tamron 2x TC (which was also designed for long tele lenses) I am strongly considering testing the 1.4x sigma with my tamron 200-500F5.6 (model 31A) zoom.